The present invention relates to devices and techniques for transduction of electrical energy into mechanical energy, and vice versa. These devices and techniques are employed in the design of amplifiers, modulators, detectors amd filters through performance of signal processing functions acoustically rather than electronically.
Devices for transduction of electrical signals into bulk acoustic waves are known in the prior art. However, bulk devices have heretofore suffered from the disadvantage that bulk acoustic waves have been unavailable for processing during delay in a substrate until such waves emerge at an output transducer.
Devices for transduction of electrical signals into surface acoustic waves are also known in the prior art, and such surface acoustic waves are available for processing during delay. However, surface acoustic wave (SAW) devices are useful over a much smaller range of wavelengths compared with bulk devices.
Spurious generation of bulk waves by interdigital surface acoustic wave transducers has previously been studied extensively (l-6). In two recent publications (5,6) the available theoretical and experimental data on bulk wave radiation in surface acoustic wave devices have been reviewed and some techniques for their reduction and control have been suggested. Bulk wave generation by microacoustic devices has heretofore been regarded as a nuisance because of the interference of bulk waves with detection of surface waves, and because it has been thought that bulk waves cannot be tapped for processing prior to their emergence from the substrate.
1. Wagers, R. S., "Analysis of acoustic bulk mode excitation by interdigital tranducers", Applied Physics Letters, vol. 24,no.9, pp.401-403, 1 May 1974. PA1 2. Milsom, R., J. Heighway, N. Reilly and M. Redwood, "Comparison of exact theoretical predictions and experimental results for interdigital transducers", Proc. of IEEE Ultrasonics Symposium, Milwaukee, Wisconsin 1974, pp. 406-411. PA1 3. Daniel, M. R., "Acoustic radiation from a high coupling cut of lithium niobate", Journal of Applied Physics, vol. 44, no. 7, pp. 2942-2945, July 1973. PA1 4. Daniel, M. R., P. R. Emtage and T. deKlerk, "Acoustic radiation by interdigitated grids on LiNbO.sub.3", Proc. of IEEE Ultrasonics Symposium, Boston, Mass., 1972, pp. 392-395. PA1 5. Mitchell, R. F., "Spurious bulk wave signals in acoustic surface wave devices", Proc. of IEEE Ultrasonics Symposium, Milwaukee, Wisconsin, 1974 pp. 313-320. PA1 6. Wagers, R. S., "Spurious acoustic responses in commercial crystals used for acoustic surface wave devices", Texas Instruments Inc., Advanced Technology Laboratory Technical Report, TR-08-75-15, Mar. 26, 1975.